1. Field of the Invention
The present invention relates to a method used in a wireless charging system and related wireless charging device, and more particularly, to a method of improving the security of the power receiver in a wireless charging system and related wireless charging device.
2. Description of the Prior Art
With the proliferation of portable electronic devices such as smart phone and tablet PC, the demand for charging devices, especially for those provided in public areas, is increasing. In addition, people would like to get rid of annoying wires if possible. One technology which realizes this desire is wireless charging, in which mobile device(s) (i.e. power receiver) is placed on and charged through a charging device (i.e. power transmitter). Therefore, the current trend is towards providing wireless charging in public areas so that people can easily find a wireless power supply to charge their portable electronic devices.
Wireless Power Consortium (WPC) is a leading organization in the world to define wireless charging specification. The document Wireless Power Transfer—Volume I, part I in version 1.1.1 released in July 2012 has specified the communication protocol between a power transmitter and a power receiver. In section 5.3.3, it defines that the power receiver shall transmit the following sequence of packets:                1. An Identification Packet, which includes an identity of the power receiver if the power receiver enters an identification and configuration phase from the ping phase.        2. An Extended Identification Packet, if the Ext bit of the preceding Identification Packet is set to ONE.        3. Up to 7 Optional Configuration Packets.        4. A Configuration Packet, where the second byte (B1) and the fifth byte (B4) of the Configuration Packet are reserved bytes, and the 4 bits (b6-b3) in the third byte (B2) are reserved bits.        
On the other hand, the specification defines that the power receiver shall transmit zero or more of the Control Error Packet, the Received Power Packet, the Charge Status Packet, the End Power Transfer Packet, and Any Proprietary Packet. If the power transmitter does not know how to handle the message contained in the Proprietary Packet, the power transmitter shall ignore that message.
Furthermore, the specification defines that at any time a user can remove a Mobile Device that is receiving power. The power transmitter can recognize such an event from a time-out in the communications from the power receiver or from a violation of the Power Transfer Contract. In addition, the power receiver may stop transmitting packets to the power transmitter at any time.
From the above description, the specification defines that the Identification Packet is sent from Power Receiver to the power transmitter only once at the identification and configuration phase, and it supports to remove the power receiver at any time. But how the power transmitter knows the power receiver is removed by the owner or by the others is not sure. As people place their mobile devices on a power transmitter, they may not always keep an eye on them. In such a situation, the mobile devices might be taken away by other people without permission.
Therefore, how to secure the power receiver while the power receiver performs wireless charging publicly is a topic to be addressed and discussed in the industry.